As a tall, skinny, and lanky mofo, let me say that the people who give me the MOST trouble are the stocky fireplug type. Shorter arms are harder to lock up.
EDIT: What Gumby said. I am honestly more comfortable in guard than on top. Don't give us any feet or legs to hook, because they will get hooked. Also, make sure to control our hips and legs when you hold top position. I love taking the back from under N/S.